Re: sc_prohibit_*_without_use

[Jim Meyering]

Bruno Haible wrote:
> Would it be possible to generalize the sc_prohibit_*_without_use rules
> to more header files easily?
>
> # Don't include this header unless you use one of its functions.
> sc_prohibit_error_without_use:
>         @h='error.h' \
>         re='\<error(_at_line|_print_progname|_one_per_line|_message_count)? 
> *\('\
>           $(_sc_header_without_use)
>
> How about generating the list of identifiers that are declared in a header
> file (macros, variables, functions, type, struct names, union names,
> enum names, enum tags) and compute a regular expression that matches them?
>
> For the first part, one could use 'ctags'?

Good idea.

> Or, if only 'extern' declared
> entities matter, one can use this script that I use in libunistring:
> http://git.savannah.gnu.org/gitweb/?p=libunistring.git;a=blob;f=lib/declared.sh

For some headers, extern symbols is enough.
For others, there are no extern symbols and rather only macros.
In general, everything matters: types, macros, extern definitions.
It'd be great to automate something.

> Also, it would be useful to extend this to POSIX header files, such
> as <stdlib.h> or <unistd.h>, by making use of the info found in
> glibc/conform/data/*.h-data.

Here's an example where I used Regexp::Assemble to generate the regexp:

# Don't include xalloc.h unless you use one of its functions.
# Consider these symbols:
# perl -lne '/^# *define (\w+)\(/ and print $1' lib/xalloc.h|grep -v '^__';
# perl -lne '/^(?:extern )?(?:void|char) \*?(\w+) *\(/ and print $1' 
lib/xalloc.h
# Divide into two sets on case, and filter each through this:
# | sort | perl -MRegexp::Assemble -le \
#  'print Regexp::Assemble->new(file => "/dev/stdin")->as_string'|sed 's/\?://g'
# Note this was produced by the above:
# _xa1 = \
#x(((2n?)?re|c(har)?|n(re|m)|z)alloc|alloc_(oversized|die)|m(alloc|emdup)|strdup)
# But we can do better, in at least two ways:
# 1) take advantage of two "dup"-suffixed strings:
# x(((2n?)?re|c(har)?|n(re|m)|[mz])alloc|alloc_(oversized|die)|(mem|str)dup)
# 2) notice that "c(har)?|[mz]" is equivalent to the shorter and more readable
# "char|[cmz]"
# x(((2n?)?re|char|n(re|m)|[cmz])alloc|alloc_(oversized|die)|(mem|str)dup)
_xa1 = x(((2n?)?re|char|n(re|m)|[cmz])alloc|alloc_(oversized|die)|(mem|str)dup)
_xa2 = X([CZ]|N?M)ALLOC
sc_prohibit_xalloc_without_use:
        @h='xalloc.h' \
        re='\<($(_xa1)|$(_xa2)) *\('\
          $(_sc_header_without_use)